JP2008155086A - Waste water treatment method and apparatus and microbial agent for waste water treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste water treatment technology which has no expense problem of an additive, and can efficiently stably perform oxidation and denitrification of ammonia. <P>SOLUTION: Oxygen is supplied to waste water in presence of nitrifying bacteria and denitrifying bacteria to carry out oxidation treatment where ammonia nitrogen contained in the waste water is converted into nitrite nitrogen by the nitrifying bacteria and denitrification treatment where the nitrite nitrogen and ammonia nitrogen are converted into nitrogen gas by the denitrifying bacteria. While controlling the oxygen supply to the waste water so that a nitrite nitrogen generation rate of the nitrifying bacteria is equal to or less than the treatment capacity of the denitrifying bacteria, the oxidation treatment and denitrification treatment are carried out simultaneously. The treatment rate of the nitrifying bacteria is a rate-limiting factor. Termination of the treatment is detected from the measurement of dissolved oxygen concentration in the waste water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for treating wastewater containing ammonia, a treatment apparatus, and a microbial agent for wastewater treatment, and in particular, conversion to nitrogen when oxidizing (nitrification) and denitrification by allowing microorganisms to act on wastewater containing ammonia. The present invention relates to a wastewater treatment method, a treatment apparatus, and a microbial agent for wastewater treatment that can improve the stability and reliability of the wastewater and that can proceed with treatment efficiently.

  In wastewater treatment using microorganisms, ammonia contained in wastewater is converted to nitrogen gas by oxidization of ammonia nitrogen (nitrification) and denitrification of oxidized nitrogen (nitric acid, nitrous acid) by the bacteria of activated sludge. can do. This processing method can be classified as follows.

  A) A method in which ammonia is converted into oxidized nitrogen by nitrifying bacteria, and oxidized nitrogen is converted into nitrogen gas using an organic substance such as methanol as an electron donor (an activated sludge modification method, for example, see Patent Document 1 below).

  B) A method of converting oxidized nitrogen to nitrogen gas by a group of bacteria that convert ammonia to oxidized nitrogen by nitrifying bacteria and then oxidize sulfur to reduce oxidized nitrogen.

C) Oxidation of ammonia to nitrite nitrogen by nitrifying bacteria, and generation of nitrogen gas from ammonia nitrogen and nitrite nitrogen by anammox bacteria belonging to denitrifying bacteria (NH ₄ ⁺ + NO ₂ ⁻ → (N ₂ + 2H ₂ O) step to convert ammonia into nitrogen gas (see Patent Document 2 below).
JP-A-8-267087 Special table 2001-506535

  Among the above-mentioned treatment methods, the treatment method of A) is widely spread worldwide, and a highly stable prescription has been established based on many experiences. Since organic substances are required for the reduction of oxidized nitrogen, the actual treatment is generally carried out in a form applied to circulate the waste water in order to use the organic substances contained in the waste water. However, in this case, oxidized nitrogen inevitably remains. Therefore, in order to reduce this concentration, it is necessary to increase the ratio of circulating the wastewater, and the repetition rate of the treatment is increased, which increases the operating cost. Further, since the oxidized nitrogen is not completely removed even if the treatment is repeated, it is necessary to add an organic substance to the waste water from the outside when the treatment is completed, and the cost of the organic substance to be supplied arises.

  Since the treatment method B) requires the addition of sulfur, the cost for using this chemical is required.

  The processing method of C) above does not require organic substances and additive chemicals, and the amount of oxygen supply required for the processing is an amount that oxidizes half of the ammonia nitrogen at the start of the processing. Few. However, the growth speed of anammox bacteria is extremely slow, so if the cells are killed or lost due to an accident or the like, it takes a very long time to regenerate the treatment system, and it takes time to recover even if the activity once reduced is restored. Cost. Further, depending on the state of the treatment system, reduction and denitrification of nitrite nitrogen may not proceed, and production of nitrate nitrogen by oxidation may proceed, and the certainty of treatment is low.

  The present invention relates to a wastewater treatment method, a treatment apparatus, and a microbial agent for wastewater treatment used in the wastewater treatment method that can efficiently and stably oxidize and denitrify wastewater without the need for expensive chemicals and organic substances. It is an issue to provide.

  Further, the present invention provides a wastewater treatment method in which the structure of equipment used for treatment is simple, oxidation and denitrification of ammonia in the wastewater proceed simultaneously, and the treatment can be repeated without reducing the activity of denitrifying bacteria. It is an object of the present invention to provide a treatment apparatus and a microbial agent for wastewater treatment used therefor.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research, and as a result, by controlling the amount of oxygen supplied to the wastewater, it is possible to proceed with the treatment of the wastewater without causing a decrease in the activity or death of the denitrifying bacteria. The inventors have found that this is possible and have completed the present invention.

  According to one aspect of the present invention, a method for treating wastewater supplies oxygen to wastewater in the presence of nitrifying bacteria and denitrifying bacteria, and ammonia nitrogen contained in the wastewater is converted into nitrite nitrogen by the nitrifying bacteria. A method for treating wastewater that proceeds with an oxidizing treatment for conversion and a denitrification treatment for converting nitrite nitrogen and ammonia nitrogen into nitrogen gas by the denitrifying bacteria, wherein the nitrifying nitrogen production rate of the nitrifying bacteria The gist is to control the supply of oxygen to the waste water so that the denitrifying bacteria are less than the treatment capacity.

  According to another aspect of the present invention, there is provided a wastewater treatment method comprising supplying oxygen to wastewater in the presence of nitrifying bacteria and denitrifying bacteria, and converting ammonia nitrogen contained in the wastewater by the nitrifying bacteria to nitrous acid. A wastewater treatment method for simultaneously proceeding with an oxidation treatment for converting to nitrogen and a denitrification treatment for converting from nitrite nitrogen and ammonia nitrogen to nitrogen gas by the denitrifying bacteria, wherein the treatment rate of the nitrifying bacteria The gist is to limit the supply of oxygen to the wastewater so that the rate is limited.

  Furthermore, according to one aspect of the present invention, a wastewater treatment apparatus includes: wastewater, nitrifying bacteria that convert ammonia nitrogen contained in the wastewater into nitrite nitrogen, and ammonia nitrogen and subnitrogen contained in the wastewater. A treatment tank for storing denitrifying bacteria that convert from nitrate nitrogen to nitrogen gas, an oxygen supply device for supplying oxygen to waste water stored in the treatment tank, and oxygen to waste water by the oxygen supply device The gist of the present invention is to have a control mechanism for controlling the supply of water and a measuring device for measuring the dissolved oxygen concentration of the wastewater.

  Further, according to one aspect of the present invention, the microbial agent for wastewater treatment includes ammonia-oxidizing bacteria and anammox bacteria, and the treatment capacity [mol-N / h] of the anammox bacteria is nitrite nitrogen production of the ammonia-oxidizing bacteria. The gist is to have it at a rate greater than the ability [mol-N / h].

  According to the present invention, the state of the wastewater is controlled so that the denitrifying bacteria can always proliferate / activate properly, and no time is required for recovering the activity of the denitrifying bacteria. A wastewater treatment method and a treatment apparatus that can repeat wastewater treatment without delay and can perform treatment stably are provided. Further, since the cost of organic substances and chemicals added to the processing system from the outside is not increased, it is advantageous in terms of processing cost, and the structure of equipment required for processing is simple. Moreover, since continuous monitoring of ammonia and nitrite nitrogen is unnecessary, it is not necessary to equip equipment such as expensive sensors for these.

In wastewater treatment using microorganisms, when oxygen is supplied, ammonia is converted to oxidized nitrogen (nitrite and nitrate) by nitrifying bacteria (generally called nitrification). In this process, ammonia oxidizing bacteria are converted to ammonia. the process of converting the nitrite nitrogen (nitrite ^{_{reduction, 2NH 4 + + 3O 2 →}} 2NO 2 - + 4H + + 2H 2 O) and, nitrifying bacteria performing nitrating converts the nitrite nitrogen to nitrate nitrogen treatment (Nitration) proceeds. When anammox bacteria, which are denitrifying bacteria, are present in this system, anammox bacteria generate nitrogen gas from ammonia and nitrous acid (NH ₄ ⁺ + NO ₂ ⁻ → N ₂ + 2H ₂ O). if progress, most ammonia (about 90%) can be converted into nitrogen gas ^{_{(4NH 4 + + 3O 2 +}} 4HCO 3 - → 2N 2 + 4CO 2 + 10H 2 actually ^{_{O., NH 4 + + 1.32NO 2}} - +0. 066HCO ₃ ⁻ + 0.13H ⁺ → 1.02N ₂ + 0.26NO ₃ ⁻ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O, Appl. Microbiol. Biotechnol. (1998) 50, 589-596) . However, in reality, the denitrification process is not reliable, and the activity of the anammox bacteria is lowered depending on the treatment conditions, and the nitrification reaction proceeds. As a result of investigating the behavior of anammox bacteria, the present inventor has found that the activity of anammox bacteria varies depending on the concentration of nitrous acid, and the state in which anammox bacteria suitably progresses denitrification by appropriately controlling the oxygen supply to wastewater. I found that I can maintain it. In the present invention, oxygen is supplied to wastewater in the presence of ammonia-oxidizing bacteria, which are nitrifying bacteria, and anammox bacteria, which are denitrifying bacteria, to nitrify ammonia in the wastewater and convert nitrous acid to nitrogen gas. In the treatment of wastewater to be advanced, the supply of oxygen is appropriately controlled according to the treatment ability of anammox bacteria to convert nitrite nitrogen to nitrogen gas. As a result, the oxidation and denitrification of ammonia proceed simultaneously, and during this time, the active state of the anammox bacteria is well maintained, so that preparation time and labor for recovering the bacterial activity are unnecessary.

  Hereinafter, the present invention will be described in detail.

When oxygen (usually using air) is supplied to wastewater containing ammonia, ammonia oxidizing bacteria convert ammonia to nitrite nitrogen. The amount of nitrite nitrogen produced in this reaction increases with the amount of oxygen supplied, but the supply of oxygen is the treatment capacity of ammonia oxidizing bacteria (maximum oxygen consumption rate [mol-O ₂ / h]). If it exceeds, the excess oxygen exceeding the treatment rate is not consumed, but the dissolved oxygen concentration in the wastewater is increased. On the other hand, anammox bacteria produce nitrogen gas from the produced nitrite nitrogen and ammonia nitrogen, so the amount of nitrite nitrogen produced by ammonia oxidizing bacteria is the processing capacity of anammox bacteria (maximum nitrite nitrogen consumption rate) As long as [mol-N / h]) is not exceeded, all nitrite nitrogen produced is consumed by anammox bacteria, so the nitrite concentration in the system does not increase. However, the activity of anammox bacteria decreases as the dissolved oxygen concentration in the system increases, and when the nitrite concentration in the system increases, the bacteria become poisoned (if the nitrous acid concentration exceeds 20 mg-N / L, the anammox bacteria will eventually become poisonous. If an excessive amount of oxygen is supplied, the activity decreases due to the increase in dissolved oxygen concentration and the poisoning due to the increase in nitrous acid concentration causes deactivation of anammox bacteria and decrease in denitrification. Increase nitrogen concentration. Moreover, nitrifying bacteria that oxidize nitrous acid to nitric acid are likely to grow. On the other hand, if the supply of oxygen is limited to an appropriate amount, the dissolved oxygen concentration and nitrous acid concentration of the wastewater will not increase, and the anammox bacteria will work effectively. The conditions for reducing the activity due to dissolved oxygen and causing no poisoning with nitrous acid are as follows: wastewater nitrous acid concentration is 20 mg-N / L or less, preferably 10 mg-N / L or less, and dissolved oxygen concentration is 1 mg-O ₂ / L or less. Since it is preferably 0.51 mg-O ₂ / L or less, if this condition is satisfied, the anammox bacteria will act effectively. As long as the dissolved oxygen concentration of the wastewater at the start of treatment satisfies the above conditions, it is possible to prevent the increase in dissolved oxygen concentration by supplying oxygen within the range not exceeding the treatment capacity of ammonia oxidizing bacteria, but also prevents the increase in nitrous acid concentration To do this, it is necessary to consider the processing capacity of anammox bacteria. Specifically, the oxygen supply rate is adjusted so that the production rate of nitrite nitrogen by ammonia-oxidizing bacteria is less than or equal to the nitrite nitrogen treatment capacity by anammox bacteria. As a result, the production stage of nitrite nitrogen becomes rate-limiting, and the produced nitrous acid is immediately consumed by anammox bacteria, so the oxidation treatment rate by ammonia oxidizing bacteria becomes substantially equal to the denitrification treatment rate by anammox bacteria, An increase in the concentration of nitrous acid in wastewater is prevented. Therefore, since the treatment environment of wastewater is maintained in a favorable state for anammox bacteria by such control of oxygen supply, ammonia oxidizing bacteria and anammox bacteria react simultaneously in a coexisting state to cause oxidation and denitrification of ammonia. Progress in conjunction. Therefore, it is not necessary to physically divide them or to individually advance the reaction stepwise. And since the activity of both bacteria is complete | finished simultaneously when ammonia runs out, it can exclude that ammonia and nitrite nitrogen remain in the waste liquid after the process.

The range of the appropriate oxygen supply rate varies depending on the balance of the processing capacity of both bacteria. Specifically, the appropriate oxygen supply rate [mol-O ₂ / h] is determined by the fact that (a) the treatment capacity of anammox bacteria [mol-N / h] is the ability of ammonia-oxidizing bacteria to produce nitrite nitrogen [mol-N / B] when bacteria are added at a rate exceeding [h / h], the processing capacity of ammonia oxidizing bacteria (maximum oxygen consumption rate) [mol-O ₂ / h] or less, (b) the processing capacity of anammox bacteria is ammonia The oxygen supply rate is below the equivalent of the treatment capacity of anammox bacteria when it is below the nitrite nitrogen production capacity of the oxidation bacteria. By adjusting in this way, the treatment speed of the oxygen oxidation bacteria (oxygen consumption rate) ) Is below the processing capacity of anammox bacteria. In addition, 1 mol of nitrite nitrogen N is equivalent to 1.5 mol of oxygen O ₂ , and the nitrite nitrogen production capacity [mol-N / h] is the treatment capacity [mol-O _{2 of} ammonia oxidizing bacteria. / H] is 1.5 times the value.

  Regarding the setting of the oxygen supply rate, it is important to assume an appropriate value in advance from the amount and activity of bacteria in the treatment system. Specifically, the activity of cultured anammox bacteria and ammonia oxidizing bacteria (for example, the treatment capacity per sludge mass) is measured, and based on this, the above-mentioned (a ) Or oxygen supply rate is assumed according to (b). The treatment system already in use is assumed as in (a) or (b) above from the activities of ammonia oxidizing bacteria and anammox bacteria extracted by sampling from the treatment system. Since the balance of the amount of cells can vary depending on the growth during wastewater treatment, it is desirable to sample and confirm the cells collected at each treatment, and the treatment capacity may be adjusted by adding cells as necessary. . Considering the safety regarding poisoning, it is preferable that the balance of the treatment ability of the bacteria is (a), and the treatment ability [mol-N / h] of the anammox bacteria is the ability of the ammonia oxidizing bacteria to produce nitrite nitrogen [ mol-N / h] is more preferably 1.5 times or more. In the case of (b) above, it is desirable that the treatment capacity of the anammox bacteria is 0.8 times or more the nitrite nitrogen production capacity of the ammonia-oxidizing bacteria, and it is 0.5 equivalent or less with respect to the treatment capacity of the anammox bacteria. It is desirable that the oxygen supply rate be

  Since the supply rate of oxygen is set according to the treatment capacity of ammonia oxidizing bacteria or anammox bacteria, the time required for treatment varies depending on the ammonia concentration of wastewater. In order to shorten the treatment time, the treatment capacity (cell mass, activity) of anammox bacteria is increased to increase the oxygen supply rate.

  As described above, the supply rate of oxygen to the wastewater is assumed according to the bacterial cell amount and activity.

  In order to determine the appropriateness of the actual oxygen supply rate and correct the deviation, there is a direct method by constantly measuring the nitrite concentration of wastewater and monitoring the production of nitrite nitrogen. When the input amount of each bacterium is adjusted to the form of a), the suitability of the oxygen supply rate can be determined based on the measurement of the dissolved oxygen concentration of the wastewater. Specifically, if the treatment capacity of anammox bacteria is greater than that of ammonia-oxidizing bacteria, the dissolved oxygen concentration increases when the oxygen supply exceeds that of ammonia-oxidizing bacteria, but Since the generation is not excessive, at the start of processing, the appropriate supply of oxygen is more accurately performed by examining the correspondence between the oxygen supply rate and the presence or absence of an increase in dissolved oxygen concentration in the vicinity of the assumed proper supply rate of oxygen. You can determine the speed. In addition, if there is an abnormality in the oxygen supply control or if the balance of bacterial treatment capacity changes due to microbial contamination, this can be detected by increasing the dissolved oxygen concentration and can be handled before the nitrite concentration increases. It is. Therefore, in the form in which oxygen is supplied within the processing capacity of the ammonia-oxidizing bacteria according to (a) above, not only can the completion of processing be detected by increasing the dissolved oxygen concentration, but also as a means for confirming the supply of an appropriate amount of oxygen at the start of processing It is advantageous in that the measurement of dissolved oxygen concentration can be used and poisoning by nitrous acid at the time of abnormality can be avoided.

  As described above, when oxygen (air) is blown into a treatment system, that is, waste water at a supply rate in an appropriate range, ammonia and oxygen are consumed, and the resulting nitrite nitrogen is immediately consumed by anammox bacteria together with ammonia. Therefore, the dissolved oxygen concentration and the nitrous acid concentration are not substantially increased. In other words, even if a minute fluctuation due to non-uniformity can occur, there is no obvious fluctuation or continuous increase. The oxygen supply rate can be varied within an appropriate range. However, if the fluctuation is severe, the dissolved oxygen concentration becomes non-uniform and the measurement becomes inaccurate or the cells are affected. Therefore, a constant supply rate is preferable.

  When the ammonia in the wastewater is depleted, the nitrite nitrogen production reaction stops, so the dissolved oxygen concentration starts to increase due to oxygen that is not consumed. Therefore, the end of the treatment can be detected by monitoring the dissolved oxygen concentration of the wastewater, and the supply of oxygen may be stopped when the dissolved oxygen concentration increases. At the end of the treatment, the activity of the anammox bacteria may be somewhat reduced due to an increase in dissolved oxygen, but poisoning is prevented because nitrite nitrogen is consumed. When the dissolved oxygen concentration increases, ammonia oxidizing bacteria grow excessively with ammonia and oxygen in the conventional continuous reaction apparatus, but in the present invention, ammonia oxidizing bacteria do not grow because there is no ammonia when the oxygen concentration increases. Wastewater that has been treated can be separated immediately by sedimentation separation, and the next treatment can be started immediately by cells that have not been poisoned by nitrite by supplying new wastewater to the collected cells. It becomes a state. The wastewater after treatment contains nitric acid of about 10 mol% of the ammonium concentration before treatment, and the organic matter remains without being consumed, so activated sludge treatment was used for the wastewater after treatment as necessary. When denitrification treatment and oxidation treatment (decomposition of organic matter) are performed, nitrogen and organic matter can be suitably removed.

In the work surface such as the separation of bacterial cells, the amounts of ammonia-oxidizing bacteria and anammox bacteria to be introduced per unit volume of waste water are about 1000 to 10,000 mg-VSS / L, preferably 2000 to 4000 mg-VSS / L, respectively. It is convenient if it is about L. When the oxygen supply rate to the wastewater is estimated per the amount of anammox bacteria, it is generally about 2 g-O ₂ / (g-VSS · d) or less, preferably about 1 g-O ₂ / (g-VSS · d). The following feed rates are preferred, but will vary depending on the activity of the anammox bacteria.

As understood from the above-described reaction formula of oxidation / denitrification, the reaction of oxidation and denitrification using anammox bacteria requires bicarbonate ions (carbon dioxide in the air can be used). For this reason, bicarbonates such as sodium bicarbonate are added according to the state of the wastewater. The base constituting the bicarbonate is not particularly limited as long as it does not inhibit the growth and proliferation of bacteria such as heavy metals. It is preferable to add an amount of 0.1 to 2 moles of bicarbonate per mole of ammonia, depending on the ammonia concentration of the wastewater. When a metal such as sodium or a strong base is contained in the wastewater, bicarbonate ions can be introduced by blowing carbon dioxide gas and introduced into the wastewater before adding bacteria. It is also possible to use water into which carbon dioxide gas has been blown instead of bicarbonate, and a part of the waste water after treatment may be used as water for blowing. Alternatively, CO ₂ may be supplied simultaneously with supplying oxygen. That is, air can be used.

  The pH of the wastewater is slightly lowered due to the decrease in ammonia and the production of trace amounts of nitrate nitrogen. Since nitrifying bacteria that convert nitrite nitrogen to nitrate nitrogen have low activity when pH is low, it is better to treat in the neutral range or lower in terms of suppressing nitrification. Since the activity of the anammox bacteria is well maintained by the control, the pH of the wastewater does not matter so much and can be suitably carried out in the range of about pH 6-9. If the organic matter concentration (COD) in the wastewater is high, the anammox bacteria are easily driven out by the growth of bacterial groups that consume the organic matter. Therefore, the wastewater treatment according to the present invention has a COD / N ratio (mass of organic matter relative to nitrogen). Ratio) is preferably 0.3mg-COD / mg-N or less, and if it exceeds 0.3, the amount of organic matter can be removed by removing organic matter such as sludge and activated carbon. It is appropriate to apply the method A) in which nitrification and denitrification are carried out with activated sludge as described in the background section.

  Hereinafter, embodiments of the wastewater treatment in the present invention will be specifically described. The following wastewater treatment is based on a batch-type wastewater treatment device.

  The wastewater treatment device includes a treatment tank that contains wastewater, an oxygen supply device that supplies oxygen (air) to the wastewater, a measuring device that measures the dissolved oxygen concentration of the wastewater, and a gas supply rate of the oxygen supply device, such as a valve. The oxygen supply device is configured to blow oxygen gas or air into the waste water accommodated in the treatment tank using a nozzle or the like, and the dissolved oxygen concentration of the waste water is determined by the measuring device. Always measured. The treatment tank is equipped with a pipe for receiving and draining waste water and a bottom outlet used for collecting bacterial cells, and depending on the form and capacity of the treatment tank, a stirrer for making the waste water uniform as necessary May be attached. The control mechanism can be set to monitor the dissolved oxygen concentration based on the measurement result of the dissolved oxygen concentration and to issue a warning when the concentration rise is detected or to automatically stop the supply of oxygen supply It is.

  At the time of wastewater treatment, bacteria are cultured in advance to prepare ammonia oxidizing bacteria and anammox bacteria, or commercially available ones are obtained. Culture of each bacterium can be appropriately performed by a known technique according to a conventional method, and can be obtained by a known method from sludge of an existing water treatment plant that decomposes ammonia. Ammonia-oxidizing bacteria can be isolated with reference to, for example, the literature of B. Sorriano and M. Walker (J. Applied Bacteriology, 31, 493-497 (1968)). The sludge deposited with the registration number 94987 (December 12, 1987) by the Centraal Bureau voor Schimmelcultures in Baarn, the Netherlands can be used. The amount and activity of each cultured bacterium can be examined with reference to the following literature, and the processing ability of each bacterium can be understood from these.

(Ammonia-oxidizing bacteria)
Bacterial mass: Wagner M., Rath G., Amann R., Koops H.-P. and Schleifer K.-H., "In situ identification of ammonia-oxidizing bacteria", Syst. Appl. Microbiol. 18 (1995 ), p251-264.
Activity: Grunditz C. and Dalhammar G., "Development of nitrification inhibition assays using pure cultures of nitrosomonas and nitrobacter", Water Research, Vol.35 (2001), Issue 2, p433-440.
(Anamox bacteria)
Cell weight: Schmid M. et al., "Candidatus" Scalindual brodae ", sp. Nov., Candidatus" Scalindua Wagneri ", sp. Nov., Two New Species of Anaerobic Ammonium Oxidizing Bacteria", Syst. Appl. Microbiol. , 26 (2003), No. 4, p529-538.
Activity: Sliekers A. et al., "Completely autotrophic nitrogen removal over nitrite in one single reactor", Water Research, Vol. 36 (2002), Issue 10, p2475-2482.
The prepared bacteria and wastewater are thrown into the wastewater treatment equipment. In order to avoid poisoning by nitrous acid as much as possible, it is preferable to set the addition ratio of bacteria so that the treatment ability of anammox bacteria is higher than the treatment ability of ammonia oxidizing bacteria as in (a) above. The amount of bacterial cells per waste water volume is preferably about 2000 mg-VSS / L. A bicarbonate of about 0.1 to 2 mol / L of ammonia is added to the waste water. When carbon dioxide gas or air is used, it may be supplied simultaneously with oxygen supply.

Next, supply of oxygen or air is started while constantly measuring the dissolved oxygen concentration of the wastewater. If necessary, a stirring device may be used to make the waste water uniform. The oxygen supply rate [mol-O ² / h] is set according to the above (a) or (b) so that the treatment rate (oxygen consumption rate) of the ammonia-oxidizing bacteria becomes the rate-limiting factor. In the case of (a) above, the deviation between the actual oxygen supply rate and the appropriate value is eliminated based on the measurement of the dissolved oxygen concentration. For example, while measuring the dissolved oxygen concentration of wastewater, supply oxygen to the wastewater at an appropriate supply rate assumed from the amount of bacterial cells, and if a continuous increase in concentration is seen, reduce the oxygen supply rate, The supply speed with no increase in concentration is set to an appropriate value. In the case of (b) above, the oxygen supply rate is set lower than the appropriate value assumed from the amount of bacterial cells to enhance safety.

  As described above, an appropriate supply speed is determined and oxygen is continuously supplied. When the dissolved oxygen concentration of the wastewater starts to rise, the supply of oxygen is stopped and the process is terminated. The waste water is allowed to stand, the cells are settled and separated from the waste water, and the supernatant waste water is discharged from the treatment tank. The cells can start the next treatment immediately after adding new waste water. If necessary, it is preferable to sample and adjust the bacterial cell balance before resuming the treatment.

  The treated wastewater contains nitric acid with an ammonia concentration of about 10 mol% at the start, which can be removed sufficiently by performing a conventional denitrification treatment using activated sludge, and further an oxidation treatment by aeration. If applied, the contained organic matter is oxidatively decomposed, and phosphorus can be removed by uptake of phosphorus-accumulating bacteria. Since the anammox bacterium takes time to reactivate once the activity is stopped, the anammox bacterium can be continuously activated by simultaneously proceeding the oxidation reaction and the denitrification reaction according to the present invention. And stabilizes the activity of anammox bacteria.

  As mentioned above, by making the production rate of nitrite nitrogen of ammonia-oxidizing bacteria less than the treatment capacity of anammox bacteria, the oxidation of ammonia by ammonia-oxidizing bacteria becomes the rate-limiting step, so the produced nitrite nitrogen is It is immediately consumed and converted into nitrogen gas, so that the treatment rate of ammonia oxidizing bacteria and the treatment rate of anammox bacteria are substantially the same. For this reason, since inactivation of anammox bacteria can be avoided, a preparatory step for curing the bacteria and the like is not necessary, and the processing efficiency is improved. In addition, the growth and activity of anammox bacteria can be stably continued. Wastewater that is difficult to treat by the activated sludge method due to the low content of organic matter can be suitably treated, and when the ammonia concentration in the wastewater is too high, the treatment efficiency by the activated sludge method becomes extremely low. It can be suitably used as a pretreatment, and about 90% of ammonia can be removed as nitrogen gas.

  In the treatment method of the present invention, even if the ammonia concentration of the raw wastewater changes, the treatment can be performed without changing the treatment conditions such as the oxygen supply rate and the bacteria supply amount, and complicated control and monitoring of ammonia and nitrous acid are possible. The wastewater treatment can always be completed with only a slight fluctuation in the treatment time. Therefore, ammonia and nitrous acid do not remain after the treatment, and it is not difficult to settle the cells by regenerating nitrogen gas when separating the cells from wastewater. Can be efficiently separated without causing deterioration. In the conventional method, wastewater monitoring and complex control are necessary to maintain the treatment efficiency. Especially in continuous treatment, ammonia tends to remain after treatment to avoid nitrous acid and oxygen residues. In view of the fact that problems due to gas generation are likely to occur during sedimentation separation, the treatment method of the present invention is very superior to the conventional anammox treatment and is stable without the need for complicated management or special measures. It can be said that this is an advantageous method for performing the processing.

  Hereinafter, the treatment of wastewater according to the present invention will be specifically described with reference to Examples.

  Raw wastewater with an ammonia concentration of 500 mg-N / L and nitric acid / nitrite concentrations of 0 mg-N / L using a 5 L capacity treatment tank equipped with a stirrer, an aeration device as an oxygen supply means and a dissolved oxygen concentration measuring device Processing was carried out as follows.

(Example 1)
First, ammonia-oxidizing bacteria and anammox bacteria were prepared according to the aforementioned literature, and the bacterial logarithm and activity of the obtained ammonia-oxidizing bacteria and anammox bacteria were measured according to the method described in the aforementioned literature.

Raw waste water (5 L) was charged into the treatment tank, 400 g of sodium bicarbonate, ammonia oxidizing bacteria (200 mg-VSS / L, ammonia consumption rate 0.2 g-N / (g-VSS · h)) and anammox bacteria (2000 mg- VSS / L, ammonia consumption rate 0.25 g-N / (g-VSS · h)) was added to disperse the bacteria with a stirrer, and the dissolved oxygen concentration measuring instrument was started to start measuring the dissolved oxygen concentration. , 0.1 mg-O ₂ / L. The pH value of the waste liquid was adjusted to 7.5 using hydrochloric acid and caustic soda. Thereafter, the aeration apparatus was operated to adjust the air blowing rate so that the oxygen supply rate was 1.5 g-O ₂ / (L · d), and aeration of the raw wastewater was started. The dissolved oxygen concentration slightly increased with the start of aeration, but since then it was almost constant, aeration was continued. 24 hours after the start of aeration, the dissolved oxygen concentration began to rise, so the supply of oxygen was stopped and the wastewater was allowed to stand. After the bacterial cell sludge settled at the bottom of the treatment tank, the supernatant waste water was discharged from the treatment tank to obtain 4 L of discharged water. When the concentrations of ammonia, nitric acid and nitrous acid were measured, the ammonia concentration was 0 mg-N / L, the nitric acid concentration was 45 mg-N / L, and the nitrous acid concentration was 0 mg-N / L. The pH value of the discharged water was a little less than 7.

  The sludge in the treatment tank was sampled and the activities of ammonia-oxidizing bacteria and anammox bacteria were examined, and it was confirmed that the ratio of treatment capacity did not change so much. After adding 4 L of raw wastewater to the treatment tank, it was confirmed that ammonia could be oxidized and denitrified in the same manner by repeating the same treatment operation as described above.

(Example 2)
The following operations were performed using the ammonia-oxidizing bacteria and anammox bacteria prepared in Example 1.

Raw waste water (5 L) was charged into the treatment tank, 400 g of sodium bicarbonate, ammonia oxidizing bacteria (100 mg-VSS / L, ammonia consumption rate 0.2 g-N / (g-VSS · h)) and anammox bacteria (3000 mg- Add VSS / L, ammonia consumption rate 0.25g-N / (g-VSS · h)) and disperse the bacteria with a stirrer, then start the measurement of dissolved oxygen concentration by operating the dissolved oxygen concentration meter As a result, it was constant at 0.1 mg-O ₂ / L. The pH value of the waste liquid was adjusted to 7.5 using hydrochloric acid and caustic soda. Thereafter, the aeration apparatus was operated to adjust the air blowing rate so that the oxygen supply rate was 1.5 g-O ₂ / (L · d), and aeration of the raw wastewater was started. Since the dissolved oxygen concentration continued to increase slightly due to aeration, when the oxygen supply rate was immediately reduced to 1.0 g-O ₂ / (L · d), the dissolved oxygen concentration was almost 0.3 mg-O ₂ / L. Since it became constant, aeration was continued at this supply rate. 33 hours after the start of aeration, the dissolved oxygen concentration began to rise, so the supply of oxygen was stopped and the wastewater was allowed to stand. After the bacterial cell sludge settled at the bottom of the treatment tank, the supernatant waste water was discharged from the treatment tank to obtain 4.1 L of discharged water. When the concentrations of ammonia, nitric acid and nitrous acid were measured, the ammonia concentration was 0 mg-N / L, the nitric acid concentration was 42 mg-N / L, and the nitrous acid concentration was 0 mg-N / L. The pH value of the discharged water was a little less than 7.

  The sludge in the treatment tank was sampled and the activities of ammonia-oxidizing bacteria and anammox bacteria were examined, and it was confirmed that the ratio of treatment capacity did not change so much. After adding 4.1 L of new raw wastewater to the treatment tank, it was confirmed that ammonia could be oxidized and denitrified in the same manner by repeating the same treatment operation as described above.

Claims (11)

  Oxygen is supplied to the wastewater in the presence of nitrifying bacteria and denitrifying bacteria, and the nitrifying bacteria convert the ammonia nitrogen contained in the wastewater to nitrite nitrogen by the nitrifying bacteria, and the nitrite nitrogen by the denitrifying bacteria And a denitrification process for converting ammonia nitrogen to nitrogen gas, wherein the nitrite nitrogen production rate of the nitrifying bacteria is reduced to the treatment capacity of the denitrifying bacteria or less. A method for treating wastewater, characterized by controlling the supply of oxygen.   Oxygen is supplied to the wastewater in the presence of nitrifying bacteria and denitrifying bacteria, and the nitrifying bacteria convert the ammonia nitrogen contained in the wastewater to nitrite nitrogen by the nitrifying bacteria, and the nitrite nitrogen by the denitrifying bacteria And a denitrification process for converting ammonia nitrogen to nitrogen gas simultaneously, characterized in that the supply of oxygen to the wastewater is limited so that the treatment rate of the nitrifying bacteria becomes rate-limiting. Wastewater treatment method.   The wastewater treatment method according to claim 1 or 2, wherein the nitrifying bacteria include ammonia oxidizing bacteria, and the denitrifying bacteria include anammox bacteria.   The wastewater treatment method according to any one of claims 1 to 3, wherein the dissolved oxygen concentration of wastewater while oxygen is supplied is constantly measured, and the supply of oxygen is stopped when an increase in the dissolved oxygen concentration is detected. The processing capacity [mol-N / h] of the denitrifying bacteria is larger than the nitrite nitrogen production capacity [mol-N / h] of the nitrifying bacteria, and the supply rate of oxygen is the processing capacity [mol- of the nitrifying bacteria]. O ₂ / h] or less. The method for treating wastewater according to any one of claims 1 to 4.   The processing capacity [mol-N / h] of the denitrifying bacterium is equal to or less than the nitrite nitrogen generating capacity [mol-N / h] of the nitrifying bacterium, and the supply rate of oxygen is the processing capacity of the denitrifying bacterium. The processing method of the wastewater in any one of Claims 1-4 used as an equivalent or less with respect to this.   The wastewater treatment method according to claim 5, wherein the oxygen supply rate is adjusted based on whether or not the concentration of dissolved oxygen in the wastewater increases due to the supply of oxygen. Waste water, nitrifying bacteria for converting ammonia nitrogen contained in the waste water into nitrite nitrogen, and denitrifying bacteria for converting ammonia nitrogen and nitrite nitrogen contained in the waste water into nitrogen gas A treatment tank;
An oxygen supply device for supplying oxygen to the wastewater stored in the treatment tank;
A control mechanism for controlling the supply of oxygen to wastewater by the oxygen supply device;
A wastewater treatment apparatus comprising a measurement device for measuring the dissolved oxygen concentration of the wastewater.   The wastewater treatment apparatus according to claim 8, wherein the control mechanism controls supply of oxygen by the oxygen supply apparatus so that a nitrite nitrogen production rate of the nitrifying bacteria is equal to or less than a treatment capacity of the denitrifying bacteria.   The wastewater treatment apparatus according to claim 8, wherein the control mechanism controls supply of oxygen by the oxygen supply apparatus so that a treatment rate of the nitrifying bacteria becomes rate-limiting.   The ammonia-oxidizing bacterium and the anammox bacterium are characterized by having a treatment capacity [mol-N / h] of the anammox bacterium that is larger than a nitrite nitrogen-producing ability [mol-N / h] of the ammonia-oxidizing bacterium. Microbial agent for wastewater treatment.